In the roofing industry, a roofing underlayment is typically applied to the deck of a roof prior to application of shingles or other roofing material. The primary goal of the roofing underlayment is to shield the roofing deck from asphalt (from the back surface of shingles) which otherwise would necessitate tearing up the whole deck instead of just the shingles—a costly option—at the time of reroofing. Underlayments can also help to reduce “picture framing” in which the outline of the deck panels caused by irregularities in the deck surface may be visible through the roofing material applied to the roofing deck.
In most cases, the roofing underlayment comprises a felt material composed of cellulose fibers, glass fibers and a mixture thereof that is saturated with a bituminous material such as asphalt, tar or pitch. Roofing underlayments that are saturated with a bituminous material are thick composites (typically 20 to 60 mils thick), which can be hazardous to manufacture due to the presence of a flammable bituminous material. Many of the asphaltic underlayments available in the market tend to wrinkle after being applied to a roofing deck. This is especially the case if the underlayments are rained upon. Other common problems are blowing off due to wind (when shingles are yet to be installed) or the formation of splits lengthwise in the underlayments when they are left exposed for several days.
In addition to bituminous-containing underlayments, the roofing industry has also developed non-bituminous, i.e., non-asphaltic, underlayments. The prior art non-bituminous underlayments typically include Triflex 30 (a product made by Flexia Corp. and marketed by W. R. Grace), Titanium UDL (marketed by Interwrap, Inc. of Canada), RoofTopGuard II (marketed by Classic Products, Inc and Drexel Metals), Kaye-Flex UDL (from Kaye Industries, Florida), etc.
Currently, all non-asphaltic underlayments tend to be water-resistant but substantially non-breathable. That is, the non-asphaltic underlayments do not allow air or water vapor to pass through it. As a result, the moisture from the interior of the building is unable to escape to the exterior resulting in damage to the deck and roof over a number of years. Most of the non-asphaltic underlayments also tend to be slippery, especially when wet.
Furthermore, existing breathable underlayments are generally of three types: (1) micro-perforated or (“micro-perfed”) types in which a coated fabric has mechanical perforations to allow moisture vapor to escape from the building structure; (2) microporous types in which a breathable polyolefinic film is sandwiched between two or more layers by means of thermal or ultrasonic or adhesive lamination methods; or (3) a monolithic film extruded using thermoplastic polyurethane or copolyester or its blend resins which provide breathability and waterproofness in a composite structure.
Existing micro-perfed films, however, fail the water shower test as mandated by ASTM D 4869-00. Existing microporous films and monolithic film based concepts—while providing breathability as well as waterproofness—are limited by the properties of the film itself. Hence, tailorability of properties is severely limited especially in the case of monolithic film concepts since resin blend compositions required for a particular breathability and mechanical properties can be difficult to predict. Extrusion coated film may act as a waterproof barrier, a breathable layer, as well as bonding agent between the two protective layers. However, in such cases, the breathability is severely limited (usually less than 10 perms). Additionally, such extrusion coatings tend to be prohibitively expensive.
In view of the drawbacks mentioned above with prior art non-asphaltic breathable underlayments, there is a need for providing a non-asphaltic roofing underlayment that is breathable thereby allowing moisture to escape from inside the building, while preventing water and/or moisture from entering the building. In addition, skid-resistance is a highly desirable property of an underlayment to avoid injuries from roofers sliding off of the roof. Also, sealing around nails or other roof penetrations would provide additional protection towards waterproofing the system.